Method of making the same



Reissued July 24, 1951 PHENOL-ALDEHYDE SEALING AGENT AND METHOD'OFMAKING THE SAME Stewart S. Kurtz, Jr., Merion, and James S. Sweely,Swarthmore, Pa., assignors to Sun Oil Company, Philadelphia, Pan, acorporation of New Jersey No Drawing. Original No. 2,457,160, datedDecember 28, 1948, Serial No. 609,927, August 9, 1945. Application forreissue May 12, 1951,

Serial No. 226,064

13 Claims.

This invention relates to scaling agents [and the preparation thereofand more particularly to improved sealing compositions] adapted forplugging porous subterranean formations to a method of preparing suchsealing agents mid to -a method of utilizing such sealing agents withina borehole for plugging a porous formation.

The novel sealing agents of the present invention comprise an aqueoussuspension of thermosetting resin partially condensed to a particularstage of condensation, as hereinafter fully described, and capable offurther condensation to a hard infusible stage.

In the drilling of wells for oil, gas or other fluids the well boretraverses numerous formations or strata of varied porosity, such ascavernous limestone, gravel beds, oil-bearing sands, cavernoussandstones, water-bearing sands, gasbearing sands and the like. It isfrequently necessary or desirable for one reason or another to seal offcertain of these formations from theborehole and many methods foreffecting such sealing have been proposed. In drilling by the rotarymethod a drilling mud is circulated during the, general drillingoperation down through the drill" ever, that the formations areencountered which are sufficiently porous that the mud fluid passes intothe formation so that little or no mud returns to the surface. Thiscondition, which is known as lost circulation, may also be due to abreakdown of one or more of the formations traversed, caused by the highhydrostatic pressure exerted by the mud column on the formation as whenthe mud fluid has been heavily weighted with weighting material. In suchcases steps must be taken to seal off the porous formation and preventthe loss of mud fluid. Again, it is often desirable to plug off certainstrata in order to prevent or minimize ingress of undesirable fluidsinto the well. For instance, it may be desired to seal off water-bearingsands to increase the ratio of oil to water production.

Formerly it was general practice to accomplish such sealing operationsby pumping cement grout into the well, forcing it into the porousformation,

permitting it to harden in place and then drilling through the cementremaining in the borehole. Although in the case of lost circulation ithas become customary more recently to add special sealing agents such asground sugar cane stalks, mica or Cellophane to the drilling fluid toimprove its Matter enclosed in heavy brackets appears in the originalpatent but forms no part of this reissue specification; matter printedin italics indicates the additions made by reissue.

in the borehole in order to insure sealing of the porous formation. Itfrequently happens that in drilling through the hardened cement the holebecomes sidetracked into the adjacent formations, thus requiringredrilling of all the hole below the point of sidetracking, perhapsincluding the zone of lost circulation. Similar disadvantages accompanythe use of cement in sealing off water sands. A further disadvantage mayarise due to the possibility that, in some cases, the cement may beforced into the oil-bearing formation to a distance sufficient to makeit diflicult or impossible subsequently to open the formation forproduction by the usual gun perforation methods.

More recently the use of resin-forming liquids capable of condensing toa solid resin under the influence of the formation temperature in placeof cement has become known and has attained a limited applicabilityparticularly in sealing water-bearing sands. While such resin-formingliquids offer certain advantages over cement, such as greater fluidityresulting in improved sealing properties and better resistance tonatural brines and to acid such as used in acid'izing wells, they failto overcome the above-discussed disadvantages which accompany the use ofcement. Like cement, these resin-forming liquids solidify in ,-theborehole, necessitating redrilling of that portion of the hole whichthereby becomes plugged.

A1so,due to the greater fluidity of the resin-forming liquids ascompared to cement grout, they are even more apt to penetrate anoil-bearing stratum to such extent that subsequent opening ofthe stratumfor production becomes impossible. A further disadvantage of this typeof sealing agent arises when there are substantial variations inpenetrability of the earth surrounding the portion of the borehole to besealed off, as occurs in the case of a highly porous formation adjacentto a less porous formation or as may be caused by crevices within aformation. In such cases a very large amount of the resin-forming liquidmay be forced into the more penetrable portions of the surrounding earthbefore an effective seal of the less penetrable portions is obtained,with the result that the expense involvedv in carrying out the sealingoperation becomes excessive.

The present invention is directed to and pro- "tially? larger than the"dispersed "resin "particles, "Further,this resin plug under theinfluenceof .heatwilrcondense toahard:sheath-impervious toatirillingyfluids and having considerable' mechanical strengthasdistinguished from a" crumi lyr or powdery resin layer.

vides an improved sealing agent-which rovercomes the above-discusseddisadvantages of sealing agents heretofore employed. The novel sealingcompositions according to this invention" comprise a suspension of a.thermosetting resin in water, the resin being partially'condensed. to aparticular intermediate stage requisite to im-' part to the suspensionthe desired sealingcharacteristics. This particular stageof condensationmay be described as an "intermediate plastic solid stage. The partiallycondensed resin corresponding thereto is dispersible-inwater, byconventional mechanical meansand without the aid of an emulsifyingagent, to a state which is substantially non-coalescing for at leastfive hours, i. e. the dispersed resin particles do not coalescesubstantially when the suspension is permitted to stand for this periodof time.

Within this rznarticularastageof ;.condensation there is a preferredcondensation range at which theresin is capable ,of forming a suspensionwhich is substantially. permanently 'stable' with respect; tocoalescence-of ,the dispersed 'resinpar- ...ti'cl es. The suspensionobtainedby dispersingin I .watergthe resin corresponding to theaforesaid particular. intermediate .plastic solid stage, Whichsuspension constitutesthe sealing agent of" the present invention, ischaracterized" by its ability,

Qwhen-forced into a bedof granular material ,su'ch assand or gravelhaving void spacesnsub st antial1y' larger. than the, size of thedispersed resin particles, .tojform; airesin plugat the face of thebed,vwhich, upon application of heat, will condense to a hard layernon-porous to drilling fiuids. ',In other,words,',the suspension iscapable of .forming-a'resin plug or sheath at theface" of 'a porousbody;without any considerable- -penetration, of the resin intothebody'evenithough ;.the latter has pores or voids which, are" substan-The, aqueous suspensions, of the present inven 'tionhave the greatadvantage 'over previously ,known sealing agents of not forming adifficultly fdrillable solid masswithin the iwell'bore. While 'the'resin(particles of the suspension which remains: in the borehole maycoalesce: to aniextent With time; the coalesced resin upon curing underborehole conditions 'does not becomeithe hard .solidmass that isobtainedwhen a resin-forming (liquid or cement'grout, is, used "as thesealing agent. Furthermore, after .theiresinlayer has "been plasteredout:on' theiborehole wall,;-setting ,of'unplastered-resin to a solidmass within the borehole 1 may ,be minimized or prevented by jfl ushingout the suspension before the resin has 1 haditime to :cure.

This may be accomplished by' circulating a streamvof water into and out;of

.theborehole;preferably'slowly to, insure against the possibility offlushing out artof .the plas- .tered resin layer. Thegresin. layerremainingon quarter'to one inch thickness. j.Thus, any oil- ;bearngstratum which has beensealed off; may ,rea'dilypbe openedflup. forproduction by thev usual u,nj perforation method. 'A further, advantageresults. from the ability of the suspension to plaster out.,at.the.facevof. evena veryporousifor- -;,mation, such as one-quarter inch,:gravel,since this characteristic prevents deep penetration of the resin intothe formation and thus reduces to a minimum the amount of resin requiredto 5 obtain an effective seal. Also the fact that the sealing agentwhich remains in the borehole" is composed partly of water instead ofentirely of resin further reduces the amount of resin required forcarrying out the operation.

As starting materials for producing the partially condensed resin, it ispreferred to use reactantsnfzthe phenol-formaldehyde type andparticularly phenol and formaldehyde. However; other materials capableof forming thermosettingresins may be employed to produce satisfactorysealing agents according to the invention. Among other types ofthermosetting resins which are .usefulmay .be, mentioned theifollowing:,ureai-formaldehyde, :melamine formaldehyde, and phenol-furfural resins.With all such types the successful preparation .of a suspension suitable.as a sealing agent depends on carrying the condensation reaction tothat particular intermediate plastic solid stage which we havefoundprovides, the characteristics required of the present; products.

The first step in the procedure *of'preparing the sealing agentcomprises reacting the starting material under condensation conditionsto the desired stage. Selection of the proper'reaction conditions, such-as the proper quantities of reactants, the type ..and amount ofcatalyst "and the -reaction temperature, will depend on the I particularreactants employed. Since the preparation of thermosetting resins iswell known, the'proper" selection of, reaction conditions for anyparticular case will be readily within the skill of the" art. Some ofthe aforesaid starting materialsare known to: react slowly whileotherstend-to react very rapidly. It is primarily necessary-that conditions bechosen so that there- 'action-iwill"proceedat arate such'that it can he;stopped when the properstage of partial-con- =densation is reached.

In'an earlystageof the reaction, the: product -is-still liquid.While-this form, ofproduct can :be dispersed-in-water;the dispersedresin rap- "'i'dly coalesces', thus requiring a good emulsifying'"agent'ifa relatively stable suspension is to'be 50 formed. fWhenanon-coalescing dispersion is obtained byemploying such emulsifyingagent,

"theresulting emulsion-is-so-stable as to-lack the [ability to' functionproperly-as a sealing agent, {the resin particles merely; passingthrough a poal-rous material such assand or gravel.

- "-"In a further stage of the reaction a stickysemiliquid"-isqobtained-which cannot be dispersed by 'imeansofa--con-ventional stirring device suchas a'mo'tor driven"agitator. Oncontinuing the re- 'aotion still further, the product takes on moreof,:a solid character-and passesthrough a stagegat iwhichitis a sticky orgummysemi-solid which is dispersiblein Water but which soon coalescesafter dispersion. If the reaction isallowed to pro- 'ceed-past*-thisstage, the resin will reach-that desired intermediate plasticsolidstageat which it is still sufiiciently soft to be dispersible inwater J byconventional means'but not so soft or gummy as'xtofail' togive asuspension which is substam tially stable for areasonabletime,such as at leastffive hours. "Preferably the reaction iscarried wellintothisintermediate plastic solid stage in order to reach.theupreferred condensation rangeatwhichthe resin isodispersible; to asub- .75 sta'ntial ly non-coalescing state.

On the other hand, if the reaction is allowed to proceed too far, theresin will become too tough orhard for the suspended particles, uponplastering and curing on sand or gravel, to fuse together properly andthereby produce a resin layer having good mechanical strength. More orless concurrently although not exactly so, the resin will tend to loseits'ability to be dispersed in the conventional manner or at least willbe dispersible only with great difliculty. The first indication,however, that the reaction is being carried past the desired stage isshown by the nature of the resin layer obtained on forcing an aqueoussuspension of the resin product into a body of sand or gravel.- Althoughthe resin ma still be suspendible and may plaster out from thesuspension at the face of the porous material, the resulting resin layerafter curing under the influence of heat will tend to have poorermechanical strength, being hard but i rittle if the reaction hasproceeded somewhat further than is desirable and .then becoming crumblyor powdery if the reaction has proceeded substantially past the desiredstage.

. The range in degree of condensation between a product which is toosoft and one which is too hard to produce a suitable sealing agent israther limited. It is important that the reaction be stopped within thisrange and preferably well within the range for this gives a productwhich is readily 'dispersible to a non-coalescing state, which willplaster out of the suspension properly yielding a resin layer which oncuring becomes a strong non-porous sheath, and which, in addition, canwithstand a reasonable amount of preheating of the suspension withoutsubstantial loss of plastering and curing qualities. This lastnamedproperty of retaining thedesired sealing characteristics even after thesuspension has been heated for a reasonable time (o. 'g., one hour at150 F. or one-half hour at 200 F.) serves, in practice to insureeffective sealing of the formation even when there is a substantialinterval between the time of introducing the suspension into theborehole and the time it reaches, and the resin plasters out on, theformation.

The final step in the preparation of the sealing agent comprises formingthe resin-inwater suspension. This may be carried out simply byvigorously mixing together the resin and water as by means of amotor-driven stirrer. In'cases where-a catalyst has been used to promotethe condensation reaction, the catalyst preferably is washed out of thepartially condensed resin at thispoint' in order to minimize furthercondensati'o'nof the dispersed resin and permit the suspension to bestored, if desired, for a reasonable time without loss in sealingquality (say, for two or three weeks at room temperature or for two orthree months under refrigeration). This may be accomplished by firstagitating the partially condensed resin with several volumes of wateruntil it is well dispersed, allowing the mixture to-stand for a shorttime sufficient to permit dis-. persed particles to settle and form aconcentrated suspensionas the lower layer, decanting the excess water,then mixing the concentrated suspension with additional quantities ofwater and repeating the procedure until substantially all of thecatalyst has been removed. The resultant concentrated suspensionobtained after final de-' cantation of excess water generally containsin the order of -60% water. This product may be permitted to stand for aprolonged period without substantial cqalesqence or the dispersed resinparticles, provided the degree of condensation of the resin is wellwithin the described range. Some of the concentrated suspensions,depending upon the particular starting materials and reaction conditionsused, exhibit thixotropic properties, i. e. they become gel-like onstanding but readily become fluid again when mildly agitated. While thisthixotropic characteristic seems to be largely coextensive with thedesired sealing properties for certain products, this is not true in allcases, since many suspensions may be prepared which have all of thedesired qualities of a sealing agent according to the invention butwhich exhibit no thixotropy.

The procedure described above applies generally for the various types ofreactants which may be used to form the thermosetting resin. Within thegeneral procedure described, some variation in specific details ofoperation will be necessary depending on the particular reactantsselected. For example, with certain starting materials a catalyst willbe required to promote the reaction while with others the reaction willproceed rapidly without a catalyst. With phenol and formaldehyde as thereactants, either an acid or alkaline catalyst may be used. Examples ofsuitable acid catalysts are hydrochloric acid, sulfuric acid, phosphoricacid and sulfanilic acid. Amongsuitable alkaline catalysts are includedsodium, potassium and ammonium hydroxides, sodium carbonate and sodiumbicarbonate. On the other hand, when urea-and formaldehyde are used asthe starting materials, the reaction occurs rapidly in the absence ofany catalyst. Again, when the starting material contains a largeproportion of water as is the case in preparing phenol-formaldehyderesins, the partially condensed resin may precipitate from the reactionmixture during the course of the reaction thus necessitating subsequentseparation of the resin from the rest of the reaction mixture. However,with material such as phenol-furfural, as also with urea-formaldehyde,all of the reaction mixture is converted into resin so that suchseparation step is not required.

. The appearance of the reaction mixture seems to be the best means ofdetermining when the proper stage of condensation has been reached. Thismeans of judging when to stop the reaction, of course, requiresexperience on the part of the operator in preparing the product.Furthermore, the appearance of the reaction mixture will vary greatlyfor different starting materials and to a lesser degree with differentreaction conditions, thus requiring that the operator be more or lessfamiliar withthe appearance of the reaction mixture at the variousstages of condensation for any given case. However, a skilled operatorafter making several runs and testing the product to see if it has thedesired characteristics will readily be able to determine the properpoint for stopping the reaction.

For thepurpose of. illustration, a more detailed description of thereaction stages observed inthe preparation of phenol-formaldehyde resinsisgiven. This class of product may be subdivided into two groups:: (1)alkali catalyzed and (2) acid catalyzed. -In preparing either type,phenol and formalin (which consists of about 40% formaldehyde in aqueoussolution) are mixed in any suitable proportions such as from one to fourpartsof formalin per part of phenol by weight, and the mixture is heatedto a suitable reaction temperature such as 100 C. in the presence of asmall amount of catalyst. At the beginning of the reaction the mixtureis a homogeneous solution having the appearance of -.water-. As thereaction proceeds it turns milky and becomes more and more opaque untila resin phase precipitates which is-fiuid even at room'temperatime. Onfurther reacting, the resin becomes less and less'fluid, passing throughastage at which it'may be avis'cous sticky fiuidat thereac'tiontemperature but a soft gummy semi-solid or solid at room tem erature. Inthis formLthe resin either is. practically'non-dispersible in wate-r byconventional-meansor, if dispersible, gives a=suspension the dispersedparticles of which readily coalesce.

Further reaction causesthe-resin to reach that intermediateplastic solidstageat which the reaction should be stopped.-- At this stage, thealkali catalyzed pr od'uctywhile at-thereaction temperature, generallyha's a gel-like appearance and a consistency much like-.set-gelatin, asmay. be -tested by insertin'g a glass rod into the'reactio'n' mixture.When cooled, this productretains? itsgel-like: appearance.- but-becomesconsiderably t'ou'glie'r although sti llpliable. In the case of tlie'acldcatalyzed product, the: resin at the reaction 'temperature has theappearance of a soft 'gu'mm'y' s'olido'r' even a sticky viscous fluidand whencooled to room temperature becomes considerably tougheri Thos'ea'cid catalyzed products which have beenreacted -well. intothe desiredstage; of condensation have. the appear ance at roomtemperature' ofanelastic or rubbery SO'Iidr If the reaction isallowed toprocee'd stillfurthen, the product" becol'ne's tougherand more difficult to suspend-As previously described, the

best evidence of passingtthe desiredstage'of condensation is reflectedin the nature of the-resin plug obtained by forcing asuspension ofthepr'odnot into sand or gravel and permitting the resin 1ayertocure-under the influence of heat. Ifthe degree;- of condensation isbeyond, -but-'not too far beyond; the preferred stage, the cured resinplug or sheath obtained will: still be non-porous but will have abrittle2= Furtherreactionwill cause the resin l u become crumbly andeventually orous" and powderyen during; At the-same time,iii-willbecomeinoreandmore difficult to effect? dispersion oI- theresin,until finally the'reslii will reac-h such estate of hardness that, forall practical purposes,- it willbenon-dispersiblL- "Flie -followingexamples; in which" parts are by weight; serve -to illustrate theinvention more specifically:

EXAMPLE, 1.

driven" stirrer and the temperature Wasi-ma-intalned atabout 95Cabyzmeans of aconstant temperature bath. surrounding the-reaction ves-'sel... Afterthe reaction-had been.:stopped; the resinwas separatedfromthe rest of. the reactionmtnre-eand-ithe separated. testedofordispersibility and-sealing qualitiesQ-The ability to formanon-coalescing suspension was determined by mixingwith water in themanner de: scribed hereinbefore, during which step the 'c'ata' lyst waswashed-out of the resin by mixing w ith water and decanting the excesswater several times. The sealing qualitieswere determined by for ei-ngthe resulting suspension into a bed of 10 mesh sand, th'encuring theresin filter cakeat'za temperature of 200" F. and observing the: cl-taracter oi -the cured-cane. The followingaresults Were obtained:

Reactiohtime=160 minutes: The resin,': wh ieh separatedfrom solutiononly after the. reaction r mixture was cooled,- was a sticky viscousliquid and could not be suspended.

Reaction time=l minutesz .The' resinsepa ratedasa viscous liquid phaseat reaction ternperature and-became av soft sticky solid when cooled-This product, although dlfiiCl-llt to disperse'; could be suspended butthedispersedparticles 'coalesced. when the suspension was allowed tostand overnight.

Reaction time= minutes: The resinwasless sticky than: in the previousrun and-formed a substantially non-coalescingsuspension. The productgavea filter cake whichcured in 7- hours to a hard non-porous layer.

Reaction time=-l90 minutes The resin was a gelatinoussolid whichtoughened considerably-Jon cooling to room temperature. It formed anoncoalescing thixotropic suspension capable of plastering out andcuring to a hard non-porouslayerin 5 hours. Precuring of the suspensionfor one half hour at 200 F. before filtration reduced-the cure time tothree hours and caused only a slight decrease in strength of the curedfilter cake.

Reaction time=205 minutes: .Similar tominute run.

Reaction time=215 minutes: Similar. to 190 minuteruni Reaction time=230minutes: Similar-to 1-99 minute run except that resin was substantiallytougherv andthe filter cake required a shorter time to. cure. Alsoprecuring of the suspension caused greater loss in strength, givingverybrit tle'resinlayer after the filter cake had beencured for 2 uhours at200 F. 7

Reaction time=240 minutes: Resinsomewhat tougher than in 230 minute runand more difli cult to disperse. Suspension tended to give cured filtercake which was brittle. Precuring of sus-- pension resulted in crumbly0r powdery filter cake.

Reaction time==280 minutes: Resin harderthan in 240 minute run but stillsuspendible. Suspension gave an unsatisfactory, crumbly filtercake evenwithout precuring'.

Reaction time =330 minutes: The resin was sufficiently hard that itcould not be suspended.

EXAMPLE II .Another series of runs was carried out under conditionsasdescribed in Example .I except that 0.5. part concentrated sulfuric acidwas usedas .vsea snuie att nt on emp rature-and aj ifie rnon--dispersible in the conventional manner.

semi-solid at room temperature. In two runs made under these conditions,the product was In a third run, the product was dispersible but formed asuspension in which the resin particles coalesced after the suspensionhad been permitted to stand for several hours. This shows that theconditions of this run represent about the borderline between a productwhich is practically non-dispersible and one which may be dispersed toform a suspension.

Reaction time=130 minutes: Product was a viscous liquid at reactiontemperature but less sticky at room temperature than in previous run andcould be dispersed to form a suspension which had the desired plasteringproperties butwhich coalesced on standing overnight.

Reaction time=140 minutes: Product similar to that for 130 minute run,being somewhat harder but still sticky. It formed a suspension havingvery good plastering characteristics but which coalesced on standingovernight.

Reaction time=l60 minutes: Similar to 140 minute run but product wassomewhat harder. Suspension exhibited only a slight tendency towardcoalescence and had very good plastering characteristics.

Reaction time=180 minutes: Simila to 160 minute run but dispersed resinparticles showed no tendency to coalesce. Suspension gave filter cakewhich cured to hard non-porous sheath in 1 about 45 hours at 200 F.

Reaction time=200 minutes: Product was still a ver viscous fluid atreaction temperature but a solid having relatively little stickiness atroom temperature. It formed non-coalescing suspension having very goodplastering characteristics.

Reaction time=210 minutes: Product was soft plastic at reactiontemperature and a tough elastic or rubbery solid at room temperature.

acteristics.

Reaction time=225 minutes: Product was tougher than in previous run butcould be dispersed to form satisfactory sealing agent.

Reaction time=240 minutes: Product was very tough even at reactiontemperature and was very difiicult suspend. The suspension, althoughlumpy, still had sealing characteristics but was undesirable as sealingagent.

EXAMPLE III A series of runs was made in which the ratio of phenol toformalin was varied. In each run,

one part of sodium hydroxide per 100 parts of Phenol/formalin ratio 1/1Reaction time, minutes 218 EXAMPLE IV In another series of runs in which100 parts of phenol were reacted with 300 parts of formalin in thepresence of 1 part of sodium hydroxide,

It had the desired dispersion and plastering charfor 220 minutes.

10 the following results were obtained by varying the reactiontemperature:

Temperature. C. Character of Product 913 No product formed. 903 Toosoft.

660 Satisfactory. 332 D0. 237 Do. Do.

EXAMPLE V A mixture of 100 parts of cresylic acid and 300 parts offormalin were reacted at 100 C. for 152 minutes in the presence of 1part of sodium hydroxide. The product wasa tough elastic mass at roomtemperature. It formed a non-coalescing suspension with water, whichplastered out on 10 mesh sand giving a filter cake that cured in 12hours at 200 F. to a hard non-porous layer.

EXAMPLE VI I A mixture of 100 parts of phenol, 100 parts oftrioxymethylene (paraformaldehyde) and 100 parts of formalin was reactedat 100 C. in the presence of one part of sodium hydroxide. A stickysolid resin having a curdy appearance at room temperature was obtainedafter reacting This product formed a noncoalescing suspension which gavea filter cake that cured in '7 hours at 200 F. to a hard nonporous plug.

EXAMPLE VII A mixture consisting of 100 parts of urea and 200 parts offormalin was reacted Without the aid of a catalyst for 100 minutes at95-100 C. The product, which consisted of the total reaction mixture,was a somewhat viscous liquid at the reaction temperature and became agelatinous solid when cooled to room temperature. It formed anon-coalescing suspension which gave a filter cake that cured in 2 hoursat 200 F. to a hard non-porous layer.

With urea and formalin in the proportion of 1:2, good products ma beobtained with reaction times generally within the range of about 90-250minutes. However, if the proportion of these particular startingmaterials is changed substantially, it will be difficult to obtain asatisfactory sealing agent at any reaction time.

EXAMPLE VIII A mixture of 100 parts of phenol and 200 parts of furfuralwas reacted in the presence of 10 parts of sodium hydroxide (added as a50 Be. aqueous solution) at a temperature approximating 100 C. for atotal time of 250 minutes. The product, consisting of the total reactionmixture, was a tar-like liquid at reaction temperature and a toughelastic solid at room temperature. It formed a non-coalescing suspensionwhich gave a filter cake that cured in about 34 hours at 200 F. to afairly hard layer. This product, although being useful as a sealingagent, was of poorer quality than generally desired in that the curedresin layer was somewhat porous and brittle.

EXAMPLE IX A mixture of 100 parts of melamine and 400 parts of formalinwas reacted at 95400? C. in the presence of 0.5 part of. sodiumhydroxide. The total time at the reaction temperature was minutes. Theproduct was a gelatinoussolid, very similar to the best productsobtained from I as; as

phenol-formaldehyde using analkaline catalyst.

The product formed a non-coalescing suspension which was an excellentsealing agent. This suspension gave a resin layer which cured in 5 hoursat 200 F. to a hard non-porous sheath.

When the reaction of this example is carried out without the sodiumhydroxide, the desired stage of condensation is reached in a muchshorter time. This shows that with melamine and formalin as thereactants, sodium hydroxide acts as a retarder rather than a catalyst.An excellent product also may be prepared when the sodium hydroxide isomitted, although there may be some difiiculty in stopping thecondensation at the desired stage due to the speed of reaction.

In order to obtain a cured resin sheath having good mechanical strength,it is best to employ a relatively high pressure in forcing thesuspensioninto the porous body or formation. We

have found that the use of a high pressure generally results in astronger cured resin layer than when a low pressure is used, presumablybecause of a more complete fusion of the plastered resin particles.

The sealing agents of the-present invention may be mixed with a catalystbefore'use, if desired, and the amount of catalyst may 'be'regulated soas to reduce the time of cure at the formation temperature. byintroducing the sealing agent into-the borehole and forcing it into theformation, either the concentrated suspension or a dilute suspension ofthe resin may be used. It has been found that contamination-of thesealing agent by minor amounts of drilling mud, such as may happenduring actual use of the sealing agent in a well bore, does not causeany decreasein the plastering ability of the suspension nordoes ;itcause any substantial loss in mechanical strength of the cured resinlayer. However, drill- -ing-mud in amount over 50% in the suspensionresults in a resin layer having zpoorer mechanical strength andgenerally unsatisfactory for effecting a good seal. 1

- In carrying :out the sealing Operation, a batch ,of the sealing agentis pumped into the well and to a point adjacent the desired formation, a

packer being used if desired or necessary-to place L'S'LLfthe sealingagent at the proper location. ficient pressure is applied to thesealingagent to overcome the formatimrpressure and cause filtration of thesuspension into the formation, whereby the dispersed resin particlesplaster out at or near the face of the formation. The reup through theannular space between the drill pipe and the borehole.

We are aware that it has been proposed heretofore to incorporate athermosetting resin or reactants capable of forming such resin in thedrilling fluid circulated during the general anuing operation. Thesealing agent herein. described, however, is not a drilling fluid and isnot suitable for use during the genera-ldrilling operation.

[The method of sealing a porous formation In sealing a formation 1;

.ing a ent; of the presentzinvention herein zclaimedzasrthat forms:thesubject: matter z'otzour =copending application,..Serial No.3609.;928 pflleil of xeyenrxlate l' rerewit'h. and is fully :describedand Eclaime d:'therein.-]'

'";'IAlso,].=.Sealing::agents prepared from formaldehyde andmelamine-formaldehyde;time

not;hereimiclaimed,.as theyform the :snbie'ct i'of our. copendingapplicationsrserialshlos.

. 8;fing.1fih6l1017With' formalin-in the" weight pro- "portion ofonepart of phenol to 1-4 parts: .of

formalin under ..:catalyzed1 condensation; :cond-i- '2 ti'onssto .fcrm.a thermasetting resin, conducting theureaction: through a stage atwhich. phase precipitates sand "continuing the reaction until theIesin.1..has:7reached an. intermediate plastic solid stagezat :whichitdispersiblerby "stirring in'water without the aid of an'=emuls"ifying'fagent' to form a none-colloidal suspension stable-' forat least five hours, stopping; .theiaeaction when said intermediateplasticisolidlstage is reached whereby to obtainawpartially.;.:condensed resinrcapable of further condensation to a hardinfusible stage upon application of heat, and dispersing the resin inwater 'to :form,:se;s thedesired product, a non-colloidal aqueoussuspension which, when forced into" a bed of .210 mesh sand, will form aresin sheath :at thefface of the 'bed capable of thermosetting to 'a'hard layer'non-porous to drilling fluid.

2. Method of preparing a sealing agent: for sealing porous formationswhich comprisesrareacting a reactant selected from the group consistingof phenol and cresylic acid with a reactant selected from the "group'consistingiof formalin and furfural in the weight proportion of one partof the first-named reactant 110 14 parts of the second-named reactantundercaitalyzed condensation conditions to form a thermosetting resin,continuing the reaction until the resin-has reached an intermediateplastic "solid stage at which it is dispersible by stirring in waterwithout the aid of an emulsifying agent to form anon-colloidalsuspension stable forjat least five hours, stopping thereaction when said intermediate plastic solid stage is reached wherebyto obtain a partially condensed resin capable of further. condensationto a hard infusible stage r alkaline catalyst is employed.

.5. Method according to claim 2 wherein an acid "catalyst is employed.

6. Method according to claim 2 wherein the first-named reactant isphenol andthe secondnamed reactant is formalin.

7. A sealing agent prepared. in accordance with the method defined inclaim 6.

8.1Method according .to claim .2 wherein'lthe 'firstena-med. reactant.is cresylic .acid 'I and. :the s'econd named reactant. iis formalin.

9. A sealing agent prepared in accordance with the method defined inclaim 8.

10. Method according to claim 2 wherein the first-named reactant isphenol and the secondnamed reactant is Iurfural.

11. A sealing agent prepared by the method defined in claim 10.

12. Method of sealing a porous formation trauersed by a borehole whichcomprises introducing into said borehole a sealing agent comprising anon-colloidal aqueous dispersion of thermosetting resin as hereinafterspecified, applying sufiicient pressure on said sealing agent againstthe porous formation to force water from the sealing agent into saidformation thereby plastering out a resin sheath on the borehole walladjacent the formation, and permitting the resulting resin sheath tocondense under the influence of the formation temperature to form a hardlayer impervious to drilling fluid; said dispersed resin being partiallycondensed only to that intermediate plastic solid stage at which theresin possesses the following characterizing properties: it isdispersible in water by stirring without the aid of 14 an emulsifyingagent to form a non-colloidal dispersion stable for at least five hoursand it will plaster out of such dispersion, when the same is forced intoa bed of 10 mesh sand, to

'form a resin sheath at the face of the bed,

which, under the influence of heat, will condense toa hard imperviouslayer.

13. Method according to claim 12 wherein said resin is of thephenol-formaldehyde type.

STEWART S. KURTZ, JR. JAMES S. SWEELY.

REFERENCES CITED The following references are of record in the file ofthis patent or the original patent:

UNITED STATES PATENTS

